Along with the recent development of cell technology, new culture methods to obtain cells having a function similar to an in-vivo function by mimicking an in-vivo pericellular environment or morphology have been developed. An attempt has been made to use cells cultured by such methods as a simulator for treatment or biological reaction. Various culture methods have been developed, such as a method of culturing cells using a culture support composed of a sponge or fiber; a suspension culture method in which cells are suspended in a medium so that the cells spontaneously form a spheroid; and a method of culturing cells to form a spheroid by performing a cell non-adhesion treatment on a conventional culture chamber (a flask or the like). In particular, a spheroid culture is an excellent method by which interactions of cells can be maintained, and thus the method is applied to various cells such as pancreatic islet cells, liver cells, stem cells, and cancer cells. In recent years, studies focusing on the size of a spheroid have been made. For example, in a drug screen test using cancer cells, the diameter or volume of a spheroid is used as an index (Non Patent Literature 1). It is also disclosed that cells have different functions depending on the size of a spheroid (Non Patent Literature 2 and 3). In addition to the technique of forming a spheroid as mentioned above, a technique of controlling the size of a spheroid has attracted attention. Further, since it is possible to reproduce a specific function of a cell, it is expected that this technique of controlling the size of a spheroid will be applicable in various fields, for example, the artificial organ and bioreactor fields. In such applications, a technique of preparing a large number of spheroids and recovering the spheroids is important.
As means for creating a spheroid having a uniform diameter, Patent Literature 1 discloses a method of controlling the size of each spheroid formed by changing the number of cells to be seeded in a 96WP with a U-shaped bottom on which a hydrophilic membrane is formed. However, the number of spheroids per culture area is small, and thus it is difficult to prepare a large number of spheroids. As other methods for creating a spheroid having a uniform diameter, Patent Literature 2 to 4 disclose methods of forming a spheroid in a micro-space.